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Soldier Of Fortune II Format String (Through PunkBuster)
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SUMMARY
" <http://www.punkbuster.com/> PunkBuster Anti-Cheat software technology
and services combat online cheating in some of the most popular games
being played over the Internet today. "
A format string vulnerability in PunkBuster allows attackers to crash the
Soldier of Fortune II game or execute arbitrary code.
DETAILS
Vulnerable Systems:
* PB for server version 1.180 and prior
Immune Systems:
* PB for server version 1.183
The PunkBuster server module supports the automatic kick and ban of the
players who use invalid cvars, for example with values outside the range
specified by the server.
When this situation occurs PB kicks the client abusing the game's
functions (like a clientkick command).
The message sent to the client contains both the name of the monitored
cvar and its value on the client, the resulted string is identified as
"reason".
The problem is that naturally Soldier of Fortune II makes no checks on the
"reason" parameter (watch trap_DropClient) which is passed by PB or by the
server administrator for kicking a player, so the subsequent sprintf()
call is vulnerable to a format string attack.
Normally there is no way to exploit this bug if you are not the server
administrator (typing: clientkick 0 %n%n%n%n%n) but by using PunkBuster
allows any player inside the server to crash or possibly take the control
of the remote system.
Proof of Concept:
1. launch a client
2. join a server (naturally with PunkBuster enabled)
3. type /pb_cvarlist
4. choose one of the monitored cvars like "snaps" for example
5. type: /set CVAR %n%n%n%n%n%n
example: /set snaps %n%n%n%n%n%n
6. the server will crash after some second during the kicking of the
client
ADDITIONAL INFORMATION
The information has been provided by <mailto:aluigi@autistici.org> Luigi
Auriemma.
The original article can be found at:
<http://aluigi.altervista.org/adv/sof2pbfs-adv.txt>
http://aluigi.altervista.org/adv/sof2pbfs-adv.txt
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